The overall goal of this project is to understand how the native, membrane-bound structures of three eicosanoid-synthesizing enzymes, thromboxane A2 (TXA2) synthase (TXAS), prostaglandin 12(prostacyclin, PGI2) synthase (PGIS), and the inducible microsomal prostaglandin E2 (PGE2) synthase-1 (mPGES-1) influence their enzyme functions and their functional coupling with upstream enzymes, cyclooxygenase-1 (COX-l) and -2 (COX-2) in the biosynthesis of TXA2 (a key pro-thrombotic mediator causing stroke and heart attack), PGI2 (a key anti-thrombotic mediator against stroke and heart attack) and PGE2 (a key proinflammatory mediator). PGIS, mPGES-1 and TXAS share a common substrate, prostaglandin H2 (PGH2), produced by COX-1 or -2, mainly occurring in the endoplasmic reticulum (ER) membrane. Current studies have revealed that PGIS and mPGES-1 seem to be functionally coupled with COX-2, and TXAS is functionally coupled with COX-lin the ER membrane. The mPGES-1 belongs to a family of enzymes with a different primary structure and membrane topology compared to that of PGIS and TXAS, belonging to the P450 family. This has led us to hypothesize that PGIS, TXAS and mPGES-1 have distinct modes of functional coupling with individual COX isoforms and distinct modes of interaction with PGH2 in the ER membrane. Determination of PGH2 movement (presentation) from the COXs to the downstream enzymes, and their physical proximities in the ER membrane are crucial to elucidate the mechanisms of their different functional coupling. Based on the Pl's previous funding, the new Specific Aims are proposed to: a). Identify and compare the structures and key residues in the membrane anchor domains of TXAS, PGIS and mPGES-1 involved in the PGH2 presentation influencing their biosynthesis of TXA2, PGI2 and PGE2 differently; b). Determine the membrane topology and solution structure of mPGES-1 for comparison with PGIS and TXAS; and c). Elucidate the physical proximities between the COXs and PGIS, TXAS or mPGES- 1 to establish the relationship of the physical separations and their functional couplings. The results will be achieved by using integrated biochemical and biophysical approaches; such as, recombinant proteins and high resolution NMR spectroscopy. These studies will provide insight important to understanding the molecular mechanisms in controlling the biosynthesis of PGI2, TXA2 and PGE2, which mediates vascular and inflammatory diseases, and designs of next generation therapeutic strategies.